Stationary bicycle trainers have been popular in the last few decades as a means to use an existing bicycle on a stationary device that provides resistance to pedaling without the need to also balance, as with a bicycle roller. In the current art, most bicycle trainers that do not rely on external power source, or are otherwise controlled by an electronic device, rely on some mechanical means of converting the bicyclist's kinetic energy to heat. To simulate realistic conditions of riding a bicycle on the road, it is well known that the relationship of power (the amount of resistance experienced by the cyclist) and speed is non-linear, meaning that the incremental power needed to increase speed increases with higher speed.
The most popular current means of simulating this non-linear relationship of power and speed is a fluidic clutch, much like the typical torque converter used in automatic transmissions in automobiles. Previous to the fluidic clutch, fans were popular and effective, but their popularity declined quickly after the introduction of the fluidic clutch because of the excessive noise inherent in fans. Other inventions in the past have used friction devices and magnetic devices of various architectures. The fluidic clutch devices, although mechanically simple, somewhat limit the ability of the cyclist to customize a power to speed relationship that may be desired. They are a single-stage device, meaning that the bicycle wheel drives the fluidic clutch directly. Fluidic clutch devices have a history of reliability problems because, over extended usage, the fluid seal can deteriorate, particularly in the presence of the heat that can build up in the fluid chamber.
Magnetic devices are also used, typically in a single-stage architecture, where the bicycle wheel drives a conductive plate or drum directly, and in the proximity of a fixed magnet, when the wheel drives the magnets in the proximity of a fixed conductive plate. Although inherently quiet and reliable, these have historically been limited in their ability to provide a non-linear relationship of power and speed through the full power range that is typical of realistic conditions and that professional cycling desires. Further, they typically work very well in the lower speed ranges but are limited in providing top end power at high speeds; or the opposite is true where they work well in the top end, but are limited in capability at the lower speed range. Friction devices, although capable of providing good top-end performance, will wear and change their characteristics of speed and power over time in the nominal and lower power range.